Molecular dynamics results for the diffusion of Au and Cu adatoms on ordered Cu3Au (001) surfaces were presented. It was found that, for both adatoms, there were 2 available equilibrium positions. One was located over the fourfold site, and the other one on top of a Cu surface atom. It was found that, although this second position was a temporary site rather than a stable adatom site, it played an important role in adatom diffusion. The Cu adatom diffused via various Arrhenius-type mechanisms; among which was a new type of exchange mechanism which occurred above 500K and involved second-layer Cu atoms. In addition, some interlayer Cu diffusion events were observed which were produced by the Cu adatom when localized at the on-top Cu position. It was found that the Cu adatom stimulated the creation of diffusive vacancies that contributed to rearrangement of the surface atoms. In the case of the Au adatom, it was found that its diffusive behavior was

substantially different from that of Cu adatoms. Although the Cu and Au adatoms had similar reaction paths for diffusion, the Au-adatom behavior was described by a new exchange mechanism that took place only with the participation of Cu surface atoms. This mechanism, which occurred more often above 500K, resulted in local disordering of the surface layer; thus making the Au adatom unstable. It was therefore concluded that, above 500K, the presence of Cu or Au adatoms on the Cu3Au(001) face stimulated segregation and diffusion phenomena that could be correlated with the order-disorder transition which occurred at higher temperatures.

Diffusion Processes of Au and Cu Adatoms on the Cu3Au (001) Surface. C.E.Lekka, G.A.Evangelakis: Surface Science, 2001, 473[1-2], 39-49